This invention comprises an improvement to the invention disclosed in U.S. patent application Ser. No. 06/280,597 by Carl E. Bernardi and titled "Automatic Self-Adjusting Processing Apparatus" and assigned to the assignee of this application now U.S. Pat. No. 4,364,977. The subject matter of this previous patent is specifically incorporated herein by reference and the reader is encouraged to review the Bernardi patent so as to fully understand the principles of the instant invention.
In brief, Bernardi discloses a system for the high speed spot plating of metal onto a web of material that moves intermittently through a plating head. Each time the web stops, the plating head closes about the web, clamping and sealing the web. Plating electrolyte is then directed through passageways in the head into contact with the spots on the web to be plated.
If the spots of plating are to be positioned in the exact right locations, it is necessary to accurately control the relative positions of the plating head and the web. The Bernardi patent teaches a way to do this by directing a stream of fluid from a nozzle through a hole positioned at a known location in the web. Misalignments of the hole and nozzle change the back pressure in the nozzle. The back pressure is measured and represented by an electronic digital signal. Deviations from the desired back pressure cause motors to move the plating head so as to establish a predetermined back pressure and hence the correct relative position.
Although a fluid pressure sensor is the only practical sensing system for reliable operation in the chemical environment of a plating chamber, it does present problems in that fluid pressures are slow to change relative to electronic systems and these delays can slow the entire plating process. The present invention overcomes such problems by introducing a novel method of control and calculation that efficiently copes with the fluctuating pressure inherent in the fluid pressure sensor.